A valve is a control device of a fluid pipeline. Its basic functions are to connect and cut off the circulation of a medium in the pipeline, change the circulation of the medium, change the flowing direction of the medium, and adjust the pressure or flow of the medium, so as to protect the normal operation of equipment on the pipeline. With the continuous development of modern industry, in view of the demands in aspects of petroleum, chemical industry, power stations, metallurgy, ships, nuclear energy and space navigation, higher requirements are put forward to valves and the demands are continuously increased. For one modern petrochemical plant, approximate ten thousand various valves are needed. As a result, and because valves are frequently opened and closed, the valves need to have good closing performance. Otherwise, evaporation, emission, and drip and leakage may easily occur, product quality may be low, energy consumption is increased, equipment corrodes, material consumption is increased, the environment may be polluted, and even accidents, resulting in, for example, shutdown, may happen.
At present, for most valves, in order to realize the closing function, a valve stem and a valve core need to be connected together. The valve stem drives the valve core to enable the valve core to seal the valve port. Usually, the valve stem and the valve core are fixedly connected together through threads or other manners, and these connecting manners do not allow relative movement between the valve core and the valve stem. However, in order to enable the valve to have a good closing performance, the valve core and the valve port need to be precisely fit. In order to solve this contradiction, during the production of valves, usually a method with higher machining precision and tolerance fit quality needs to be adopted. However, the effect of this method is common and the cost is higher.